Voltmeter circuit



Sept. 16, 1.94.1.

s MINNECI 2,255,211 VOLTMETER CIRCUIT Filed Oct. 25, 1940 \SYI/PI LYi rm 7 A? VOLT/46E REGULATOR REGULATED VOLTAGE CENTER VOLTAGE Inventor: Salvatore Minneci,

Patented Sept. 16, 1941 VOLTMETER CIRCUIT Salvatore Minneci, Pittsfield, Mass., assignor to General Electric Company, a corporation of New York Application October 25, 1940, Serial No. 362,805

2 Claims.

This invention relates to voltmeter circuits and more particularly to an improved arrangement for indicating the performance of automatic line drop compensated voltage regulators.

A simple automatic voltage regulator usually consists of adjustable means for varying the voltage combined with automatic means responsive to deviations in the voltage from a predetermined value for causing the adjustable means to reduce the deviations substantially to zero. Often it is inconvenient to locate the adjustable means at the place on a circuit at which the voltage is to be maintained constant and as the distance between this place and the place where it is best to locate the adjustable means is often of considerable magnitude it is also undesirable to connect the automatic means directly across the circuit at the place where the voltage is to be maintained constant and run a pilot or control circuit from this place to the adjustable means. It is therefore customary to provide many voltage regulators with a device known as a line drop compensator which in effect biases the automatic means for the effect of the voltage drop in the electric circuit between two places thereon such, for example, as the place where the adjusting means and the automatic means are connected to the circuit, and the place where the voltage is to be maintained constant. The latter is often referred to as the load center.

It is frequently desirable to be able to measure at the regulator both the regulated voltage of the regulator at this point and also the voltage at the load center. In accordance with my invention I provide a novel and simple arrangement whereby a single indicating voltmeter may be used for measuring and indicating the voltage at those two places selectively without in any way affecting the setting or operation of 'the automatic regulator.

An object of the invention is to provide a new and improved indicating voltmeter circuit.

Another object of the invention is to provide a new and improved automatic line drop compensated voltage regulator control circuit.

Theinvention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

Referring now to the single figure of the accompanying drawing I have illustrated therein diagrammatically an embodiment of my invention which is associated by way of example with an automatic feeder voltage regulator l for an alternating current distribution circuit 2. The

regulator I may be of any suitable type, such as an induction regulator or a step regulator. It is arranged to be driven in the raising and lowering directions by a reversible motor 3 whose operation is controlled by a voltage sensitive circuit controlling means 4. This means may be of any suitable type such, for example, as the monocyclic contact making voltmeter circuit described and claimed in Kuyper Patent 2,148,301 and Birchard Patent 2,167,473, both of which are assigned to the assignee of this invention. This device consists of an electromagnetic relay 5 provided with a series reactor 6 and a shunt capacitor 1. The latter two devices constitute a simple form of monocyclic circuit which has the property of converting a constant potential applied to its input terminals, namely the righthand terminal of the reactor 6 and the lower terminal of the capacitor 1 as viewed in the' drawing to a constant output current from its output terminals, namely, the terminals of the capacitor I. By means of this conversion the relay 5 is compensated for numerous errors, such as those resulting from variations in temperature and variations in impedance of the relay operating magnet.

In series with the voltage sensitive control means is a line drop compensator 8 which is shown diagrammatically in its simplest form as consisting of a resistor 9 and a reactor l0 through adjustable portions of each of which a current proportional to the current in the line 2 is circulated by means of a current transformer II. The resistor 9 and the reactor l0 may be adjusted so that their ratio corresponds to the ratio of resistance to reactance of the line 2 and their magnitudes may be adjusted to correspond to a particular length of the line 2. In this manner the voltage drop produced in the elements 9 and III will bear the same relation to the energization of the voltage responsive control means as exists between the voltage at a predetermined remote point on the circuit and the line drop between that point and the regulator. The voltage sensitive control means is energized in accordance with the regulated voltage of the regulator by means of a potential transformer 12.

With the above described arrangement the voltage of circuit 2 will automatically be maintained constant at a predetermined load center point on the circuit 2 and in so doing the regulated voltage at the point on the circuit 2 across which the potential transformer is con nected will vary with variations in load so as to compensate for the line drop between this point and the load center.

For indicating the performance of the automatic regulating system there is provided an indicating voltmeter l3. In order that this voltmeter may be made to indicate either the regulated voltage or the load center voltage I pro vide a selector switch It and a pair of resistors I5 and it.

For indicating the regulated voltage at the regulator the switch is placed in its uppermost (illustrated) position in which the voltmeter is connected through the resistor l5 across the secondary windng of the potential transformer l2. At the same tim the switch It connects the resistor I 6 across the input terminals of the voltage sensitive controlling means. The resistance of the resistor I 6 is equal to the resistance of the voltmeter l3. As the voltmeter is connected across the potential transformer I2 it is obvious that it will respond to the regulated voltage.

If now it is desired to measure the load center voltage the selector switch It is moved to its downward position. This open circuits the resistor l6 and connects the voltmeter l3 across the input terminals of the voltage sensitive controlling means. The voltmeter will therefore respond to the regulated voltage minus (vectorally) the line drop compensator voltage and this difference will correspond to the load center voltage. As the effective resistance in parallel with the input terminals of the voltage sensitive circuit controlling means has not been changed, the setting or calibration of this device will be unaffected by the operation of the selector switch The resistor I5 is equal in ohmic value to the impedance of the line drop compensator and its purpose is to secure correct indication of the regulated. voltage at no load. At no load there is of course no line. drop and consequently the regulated voltage. and the load center voltage are the same. When the selector switch is in its downward position and there is no load on the circuit the voltmeter is in effect connected across the potential transformer through the line drop compensator and as the line drop compensator is producing no compensator voltage it acts as a series impedance for the voltmeter. Therefore, in order that the voltmeter indication will be the same when the selector switch is moved to its upper position for measuring the regulated voltage at times when there is no load on the main circuit 2 it has been found necessary to use the resistor l5 to balance the efiect of the removal of the line drop compensator from the voltmeter circuit.

The resistor I5 is provided with adjustments at both ends, the right-hand adjustment being for the purpose of matching the value of the resistance IS with the impedance of the-line drop compensator and the left-hand adjustment being for the purpose of matching the voltmeter resistance with the resistance I6.

While there has been shown and described a particular embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications can be made therein What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, an electric circuit. voltage sensitive circuit controlling means connected across said circuit at a particular place thereon through a line drop compensating impedance, means for passing a current through said impedance which is proportional to the current in said circuit so as to cause said circuit controlling means to respond to the voltage at another place on said circuit, an indicating voltmeter, an impedance corresponding in ohmic value to said line drop compensating impedance, an impedance corresponding in ohmic value to said voltmeter, and means for selectively causing said voltmeter to indicate accurately the voltage of said circuit at said places for all loads on said circuit without disturbing the setting of said circuit controlling means comprising two position switching means which in one position connects said voltmeter in parallel with said voltage sensitive circuit controlling means and'in its other position connects said voltmeter acros said circuit at said particular place through said impedance corresponding in ohmic value to said line drop compensating impedance and also connects said impedance corresponding in ohmic value to said voltmeter in parallel with said voltage sensitive circuit controlling means.

2. In combination, an alternating-current power circuit, a voltage regulator for said power circuit connected therein, a primary device for controlling said regulator, a constant-potentialto-constant-current converter having input terminals connected across said power circuit so as to measure the regulated voltage of said regulator and having output terminals connected to supply energizing current to said device in proportion to the voltage across the input terminals of said converter, a line drop compensator connected in series with one of the input terminals of said converter for varying the voltage across the input terminals of said converter in proportion to the current in said power circuit so as to cause said device to respond to thevoltage at-a predetermined load center on said power circuit, a voltmeter, a resistor which is substantially equal to the resistance of said compensator, a second resistor which is equal to the resistance of said voltmeter, and means for selectively causing said voltmeter to respond to the regulated voltage of said regulator and to the load center voltage comprising two position switching means which in one position connects said voltmeter,

across said input terminals and in the other position connects said voltmeter across said power- 

